The present invention relates to an ink-jet recording unit, an ink-jet recording method and a recording head cleaning method for the ink-jet recording unit employed by electronic equipment such as a printer, a facsimile, and a copier. The present invention relates in particular to a technology which guides ink to the tip of an ink guide arranged in an ink channel to feed ink in the form of a dispersion of charged colorant particles in a solvent to agglomerate the colorant particles, applies a voltage having the same polarity as that of the colorant particles to an ejecting electrode positioned between the ink level in the ink channel and the tip of the ink guide, thereby ejecting the ink from the tip of the ink guide by way of a repulsion exerted between the ejecting electrode and the colorant particles and ejecting the ink onto a recording medium for recording onto the recording medium, and further in particular to a technology useful in preventing adhesion of colorant particles to the inner wall of the ink guide and removing the caked-on colorant particles.
As a prior art recording unit, for example a technology described in JP 10-230608 A is known. The concept of an ink-jet recording unit described in JP 10-230608 A is explained below.
FIG. 10 is a conceptual illustration explaining a recording head illustrating a prior art ink-jet recording unit. The ink-jet recording unit 40 comprises a plurality of ink guides 42 formed in a linear arrangement in a horizontal direction in FIG. 10, each formed in the shape of an inverted T so as to support by a horizontal face of a bottom section 47 a notch-shaped narrow (or trickle) channel 41 open in the vertical direction as shown to guide ink in the form of a dispersion of charged colorant particles in a solvent to a tip open by way of the capillary action, so that the narrow channel 41 will extend in the vertical direction as shown.
Further, the ink-jet recording unit 40 generally comprises a counter electrode 43 provided on recording medium support means (not shown) supporting a recording medium P in a location opposed to the tip of the ink guide 42, an ejecting electrode 45 arranged on an insulated substrate 44 in close proximity to the ink guide 42 apart from the tip of the ink guide 42, a high-voltage pulse application unit 46 for applying a high-voltage pulse having the same polarity as that of the charged colorant particles to the ejecting electrode 45, and a through hole 48 formed in the insulated substrate 44 at a position corresponding to the arrangement of the ink guide 42.
The section between the bottom section 47 of the ink guide 42 and the insulated substrate 44 functions as a channel 49 where ink flows from right to left in the figure. Thus, a bottom plate (not shown) forming a wall of the channel 49 is arranged on the bottom section 47. The ink guide 42 penetrates the through hole 48 of the insulated substrate 44. The tip of the ink guide 42 protrudes above the topside of the insulated substrate 44 as shown.
FIG. 11 is a perspective view of a recording head illustrating a prior art ink-jet recording unit. Each ejecting electrode 45 is provided in a ring shape on the topside of the insulated substrate 44 as shown to surround the through hole 48 in the insulated substrate 44.
On the ink-jet recording unit 40 of the above configuration, at least one ink guide 42 is attached to a single enclosure (not shown) to form a single recording head. At least either the enclosure of the recording head or a recording medium P is moved to relatively move each other so as to perform recording approximately all over the recording medium P.
In the ink-jet recording unit 40 of the above configuration, the ink including colorant particles travels in the narrow channel 41 and accumulates at the tip of the ink guide 42 by way of the capillary action. In this state, a high-voltage pulse is applied to the ejecting electrode 45. A repulsion exerted between the ejecting electrode 45 and the colorant particles is used to eject the ink including colorant particles in units of droplets from the ink guide 42 to allow the ink to fly to the recording medium P, thereby depositing droplets of ink and recording characters and pictures in dots.
When the high-voltage pulse is applied to the ejecting electrode 45, the ink travels in the narrow channel 41 towards the tip of the ink guide 42 by way a repulsion exerted between the ejecting electrode 45 and the colorant particles, apart from the force caused by the capillary action. While the ejecting electrode 45 is at a ground potential, the field strength in close proximity to the tip of the ink guide 42 is so low that the ink is not ejected from the tip of the ink guide 42. To the counter electrode 43 is applied a voltage having a polarity different from the polarity of the charged colorant particles. Thus, the colorant particles constituting the ink ejected from the ink guide 42 are pulled toward the counter electrode 43 so that the ink is surely adhered to the recording medium.
However, according to a prior art ink-jet recording unit, the ink in the narrow channel provided in the ink guide travels by way of the capillary action and accumulates at the tip of the ink guide. In case the ink is not ejected in this state, the solvent of the ink at the tip may evaporate thus depositing the colorant particles in the narrow channel. Deposition of colorant particles in the narrow channel disturbs the ejection thus preventing drawing of crisp images and characters on a recording medium. As the colorant particles deposit further, the amount of ink ejected from each ink guide is reduced, thus causing the dot diameter for drawing on a recording medium to be erroneous and preventing ejection of ink, which interferes with drawing.
Thus, in general, on an ink-jet recording unit, it is necessary to clean the ink channel including a recording head after drawing. However, according to a prior art recording head cleaning method for an ink-jet recording unit, the only action is to release a cleaning solution into a channel for cleaning. This cannot completely remove the caked-on colorant particles.